Protectin Conjugates in Tissue Regeneration 1 Inhibits Macrophage Pyroptosis by Restricting NLRP3 Inflammasome Assembly to Mitigate Sepsis via the cAMP-PKA Pathway.

Protectin conjugates in tissue regeneration 1 (PCTR1) is a novel anti-inflammatory and proresolving lipid mediator biosynthesized from docosahexaenoic acid. Excessive activation of NLR family pyrin domain containing 3 (NLRP3) inflammasome and consequent pyroptosis are involved in diverse inflammatory diseases. However, how PCTR1 affects NLRP3 inflammasome activation and pyroptosis are still unclear. Here, we demonstrated that PCTR1 inhibited NLRP3 inflammasome activation and pyroptosis. These results show that PCTR1 dose-dependently inhibited gasdermin D cleavage in lipopolysaccharide (LPS)-primed murine primary macrophages upon nigericin stimulation. Additionally, PCTR1 treatment after LPS priming inhibited caspase-1 activation and subsequent mature interleukin-1ß release independent of the nuclear factor-kappa B pathway. PCTR1 exerted its inhibitory effects by blocking NLRP3-apoptosis-associated speck-like protein containing a CARD (ASC) interaction and ASC oligomerization, thereby restricting NLRP3 inflammasome assembly. However, the inhibitory effect of PCTR1 could be reversed by KH7 and H89, which are the inhibitors of the cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling pathway. Moreover, PCTR1 treatment alleviated lung tissue damage and improved mouse survival in LPS-induced sepsis. Our study unveils the molecular mechanism of negative regulation of NLRP3 inflammasome activation and pyroptosis by a novel lipid mediator and suggests that PCTR1 may serve as a potential treatment option for NLRP3-inflammasome driven diseases.

Resolvin Conjugates in Tissue Regeneration 1 Promote Alveolar Fluid Clearance by Activating Alveolar Epithelial Sodium Channels and Na, K-ATPase in Lipopolysaccharide-Induced Acute Lung Injury.

Acute respiratory distress syndrome (ARDS), a common and fatal clinical condition, is characterized by the destruction of epithelium and augmented permeability of the alveolar-capillary barrier. Resolvin conjugates in tissue regeneration 1 (RCTR1) is an endogenous lipid mediator derived from docosahexaenoic acid , exerting proresolution effects in the process of inflammation. In our research, we evaluated the role of RCTR1 in alveolar fluid clearance (AFC) in lipopolysaccharide-induced ARDS/acute lung injury (ALI) rat model. Rats were injected with RCTR1 (5 µg/kg) via caudal veins 8 hours after lipopolysaccharide (LPS) (14 mg/kg) treatment, and then AFC was estimated after 1 hour of ventilation. Primary type II alveolar epithelial cells were incubated with LPS (1 ug/ml) with or without RCTR1 (10 nM) for 8 hours. Our results showed that RCTR1 significantly enhanced the survival rate, promoted the AFC, and alleviated LPS-induced ARDS/ALI in vivo. Furthermore, RCTR1 remarkably elevated the protein expression of sodium channels and Na, K-ATPase and the activity of Na, K-ATPase in vivo and in vitro. Additionally, RCTR1 also decreased neural precursor cell expressed developmentally downregulated 4-2 (Nedd4-2) level via upregulating Ser473-phosphorylated-Akt expression. Besides this, inhibitors of receptor for lipoxin A4 (ALX), cAMP, and phosphatidylinositol 3-kinase (PI3K) (BOC-2, KH-7, and LY294002) notably inhibited the effects of RCTR1 on AFC. In summary, RCTR1 enhances the protein levels of sodium channels and Na, K-ATPase and the Na, K-ATPase activity to improve AFC in ALI through ALX/cAMP/PI3K/Nedd4-2 pathway, suggesting that RCTR1 may become a therapeutic drug for ARDS/ALI. SIGNIFICANCE STATEMENT: RCTR1, an endogenous lipid mediator, enhanced the rate of AFC to accelerate the resolution of inflammation in the LPS-induced murine lung injury model. RCTR1 upregulates the expression of epithelial sodium channels (ENaCs) and Na, K-ATPase in vivo and in vitro to accelerate the AFC. The efficacy of RCTR1 on the ENaC and Na, K-ATPase level was in an ALX/cAMP/PI3K/Nedd4-2-dependent manner.

Protectin conjugates in tissue regeneration 1 restores lipopolysaccharide-induced pulmonary endothelial glycocalyx loss via ALX/SIRT1/NF-kappa B axis.

BACKGROUND: Endothelial glycocalyx loss is integral to increased pulmonary vascular permeability in sepsis-related acute lung injury. Protectin conjugates in tissue regeneration 1 (PCTR1) is a novel macrophage-derived lipid mediator exhibiting potential anti-inflammatory and pro-resolving benefits. METHODS: PCTR1 was administrated intraperitoneally with 100 ng/mouse after lipopolysaccharide (LPS) challenged. Survival rate and lung function were used to evaluate the protective effects of PCTR1. Lung inflammation response was observed by morphology and inflammatory cytokines level. Endothelial glycocalyx and its related key enzymes were measured by immunofluorescence, ELISA, and Western blot. Afterward, related-pathways inhibitors were used to identify the mechanism of endothelial glycocalyx response to PCTR1 in mice and human umbilical vein endothelial cells (HUVECs) after LPS administration. RESULTS: In vivo, we show that PCTR1 protects mice against lipopolysaccharide (LPS)-induced sepsis, as shown by enhanced the survival and pulmonary function, decreased the inflammatory response in lungs and peripheral levels of inflammatory cytokines such as tumor necrosis factor-α, interleukin-6, and interleukin-1ß. Moreover, PCTR1 restored lung vascular glycocalyx and reduced serum heparin sulphate (HS), syndecan-1 (SDC-1), and hyaluronic acid (HA) levels. Furthermore, we found that PCTR1 downregulated heparanase (HPA) expression to inhibit glycocalyx degradation and upregulated exostosin-1 (EXT-1) protein expression to promote glycocalyx reconstitution. Besides, we observed that BAY11-7082 blocked glycocalyx loss induced by LPS in vivo and in vitro, and BOC-2 (ALX antagonist) or EX527 (SIRT1 inhibitor) abolished the restoration of HS in response to PCTR1. CONCLUSION: PCTR1 protects endothelial glycocalyx via ALX receptor by regulating SIRT1/NF-κB pathway, suggesting PCTR1 may be a significant therapeutic target for sepsis-related acute lung injury.

PDX regulates inflammatory cell infiltration via resident macrophage in LPS-induced lung injury.

Inflammatory cell infiltration contributes to the pathogenesis of acute respiratory distress syndrome (ARDS). Protectin DX (PDX), an endogenous lipid mediator, shows anti-inflammatory and proresolution bioactions. In vivo, the mice were intraperitoneally injected with PDX (0.1 µg/mouse) after intratracheal (1 mg/kg) or intraperitoneal (10 mg/kg) LPS administration. Flow cytometry was used to measure inflammatory cell numbers. Clodronate liposomes were used to deplete resident macrophages. RT-PCR, and ELISA was used to measure MIP-2, MCP-1, TNF-α and MMP9 levels. In vitro, sorted neutrophils, resident and recruited macrophages (1 × 106 ) were cultured with 1 µg/mL LPS and/or 100 nmol/L PDX to assess the chemokine receptor expression. PDX attenuated LPS-induced lung injury via inhibiting recruited macrophage and neutrophil recruitment through repressing resident macrophage MCP-1, MIP-2 expression and release, respectively. Finally, PDX inhibition of neutrophil infiltration and transmembrane was associated with TNF-α/MIP-2/MMP9 signalling pathway. These data suggest that PDX attenuates LPS-stimulated lung injury via reduction of the inflammatory cell recruitment mediated via resident macrophages.

MCTR1 enhances the resolution of lipopolysaccharide-induced lung injury through STAT6-mediated resident M2 alveolar macrophage polarization in mice.

Acute respiratory distress syndrome (ARDS) is a fatal disease characterized by excessive infiltration of inflammatory cells. MCTR1 is an endogenously pro-resolution lipid mediator. We tested the hypothesis that MCTR1 accelerates inflammation resolution through resident M2 alveolar macrophage polarization. The mice received MCTR1 via intraperitoneal administration 3 days after LPS stimulation, and then, the bronchoalveolar lavage (BAL) fluid was collected 24 hours later to measure the neutrophil numbers. Flow cytometry was used to sort the resident and recruited macrophages. Post-treatment with MCTR1 offered dramatic benefits in the resolution phase of LPS-induced lung injury, including decreased neutrophil numbers, reduced BAL fluid protein and albumin concentrations and reduced histological injury. In addition, the expression of the M2 markers Arg1, FIZZ1, Remlα, CD206 and Dectin-1 was increased on resident macrophages in the LPS + MCTR1 group. Resident macrophage depletion abrogated the therapeutic effects of MCTR1, and reinjection of the sorted resident macrophages into the lung decreased neutrophil numbers. Finally, treatment with MCTR1 increased STAT6 phosphorylation. The STAT6 inhibitor AS1517499 abolished the beneficial effects of MCTR1. In conclusion, MCTR1 promotes resident M2 alveolar macrophage polarization via the STAT6 pathway to accelerate resolution of LPS-induced lung injury.

Protectin DX promotes epithelial injury repair and inhibits fibroproliferation partly via ALX/PI3K signalling pathway.

Acute respiratory distress syndrome/acute lung injury (ARDS/ALI) is histologically characterized by extensive alveolar barrier disruption and excessive fibroproliferation responses. Protectin DX (PDX) displays anti-inflammatory and potent inflammation pro-resolving actions. We sought to investigate whether PDX attenuates LPS (lipopolysaccharide)-induced lung injury via modulating epithelial cell injury repair, apoptosis and fibroblasts activation. In vivo, PDX was administered intraperitoneally (IP) with 200 ng/per mouse after intratracheal injection of LPS, which remarkedly stimulated proliferation of type II alveolar epithelial cells (AT II cells), reduced the apoptosis of AT II cells, which attenuated lung injury induced by LPS. Moreover, primary type II alveolar cells were isolated and cultured to assess the effects of PDX on wound repair, apoptosis, proliferation and transdifferentiation in vitro. We also investigated the effects of PDX on primary rat lung fibroblast proliferation and myofibroblast differentiation. Our result suggests PDX promotes primary AT II cells wound closure by inducing the proliferation of AT II cells and reducing the apoptosis of AT II cells induced by LPS, and promotes AT II cells transdifferentiation. Furthermore, PDX inhibits transforming growth factor-ß1 (TGF-ß1 ) induced fibroproliferation, fibroblast collagen production and myofibroblast transformation. Furthermore, the effects of PDX on epithelial wound healing and proliferation, fibroblast proliferation and activation partly via the ALX/ PI3K signalling pathway. These data present identify a new mechanism of PDX which targets the airway epithelial cell and fibroproliferation are potential for treatment of ARDS/ALI.

Maresin Conjugates in Tissue Regeneration 1 improves alveolar fluid clearance by up-regulating alveolar ENaC, Na, K-ATPase in lipopolysaccharide-induced acute lung injury.

Maresin Conjugates in Tissue Regeneration 1 (MCTR1) is a newly identified macrophage-derived sulfido-conjugated mediator that stimulates the resolution of inflammation. This study assessed the role of MCTR1 in alveolar fluid clearance (AFC) in a rat model of acute lung injury (ALI) induced by lipopolysaccharide (LPS). Rats were intravenously injected with MCTR1 at a dose of 200 ng/rat, 8 hours after administration of 14 mg/kg LPS. The level of AFC was then determined in live rats. Primary rat ATII (Alveolar Type II) epithelial cells were also treated with MCTR1 (100 nmol/L) in a culture medium containing LPS for 8 hours. MCTR1 treatment improved AFC (18.85 ± 2.07 vs 10.11 ± 1.08, P < .0001) and ameliorated ALI in rats. MCTR1 also significantly promoted AFC by up-regulating epithelial sodium channel (ENaC) and Na+ -K+ -adenosine triphosphatase (Na, K-ATPase) expressions in vivo. MCTR1 also activated Na, K-ATPase and elevated phosphorylated-Akt (P-Akt) by up-regulating the expression of phosphorylated Nedd4-2 (P-Nedd4-2) in vivo and in vitro. However, BOC-2 (ALX inhibitor), KH7 (cAMP inhibitor) and LY294002 (PI3K inhibitor) abrogated the improved AFC induced by MCTR1. Based on the findings of this study, MCTR1 may be a novel therapeutic approach to improve reabsorption of pulmonary oedema during ALI/acute respiratory distress syndrome (ARDS).

PCTR1 improves pulmonary edema fluid clearance through activating the sodium channel and lymphatic drainage in lipopolysaccharide-induced ARDS.

Acute respiratory distress syndrome (ARDS) is a lethal clinical syndrome characterized by damage of the epithelial barriers and accumulation of pulmonary edema fluid. Protectin conjugates in tissue regeneration 1 (PCTR1), an endogenously produced lipid mediator, are believed to exert anti-inflammatory and pro-resolution effects. PCTR1 (1 µg/kg) was injected at 8 hr after lipopolysaccharide (LPS; 14 mg/kg) administration, and the rate of pulmonary fluid clearance was measured in live rats at 1 hr after PCTR1 treatment. The primary type II alveolar epithelial cells were cultured with PCTR1 (10 nmol/ml) and LPS (1 µg/ml) for 8 hr. PCTR1 effectively improved pulmonary fluid clearance and ameliorated morphological damage and reduced inflammation of lung tissue, as well as improved the survival rate in the LPS-induced acute lung injury (ALI) model. Moreover, PCTR1 markedly increased sodium channel expression as well as Na, K-ATPase expression and activity in vivo and in vitro. In addition, PCTR1i also upregulated the expression of LYVE-1 in vivo. Besides that, BOC-2, HK7, and LY294002 blocked the promoted effect of PCTR1 on pulmonary fluid clearance. Taken together, PCTR1 upregulates sodium channels' expression via activating the ALX/cAMP/P-Akt/Nedd4-2 pathway and increases Na, K-ATPase expression and activity to promote alveolar fluid clearance. Moreover, PCTR1 also promotes the expression of LYVE-1 to recover the lymphatic drainage resulting in the increase of lung interstitial fluid clearance. In summary, these results highlight a novel systematic mechanism for PCTR1 in pulmonary edema fluid clearance after ALI/ARDS, suggesting its potential role in a therapeutic approach for ALI/ARDS.

MCTR1 alleviates lipopolysaccharide-induced acute lung injury by protecting lung endothelial glycocalyx.

Endothelial glycocalyx degradation, critical for increased pulmonary vascular permeability, is thought to facilitate the development of sepsis into the multiple organ failure. Maresin conjugates in tissue regeneration 1 (MCTR1), a macrophage-derived lipid mediator, which exhibits potentially beneficial effects via the regulation of bacterial phagocytosis, promotion of inflammation resolution, and regeneration of tissue. In this study, we show that MCTR1 (100 ng/mouse) enhances the survival of mice with lipopolysaccharide (LPS)-induced (15 mg/kg) sepsis. MCTR1 alleviates LPS (10 mg/kg)-induced lung dysfunction and lung tissue inflammatory response by decreasing inflammatory cytokines (tumor necrosis factor-α, interleukin-1ß [IL-1ß], and IL-6) expression in serum and reducing the serum levels of heparan sulfate (HS) and syndecan-1. In human umbilical vein endothelial cells (HUVECs) experiments, MCTR1 (100 nM) was added to the culture medium with LPS for 6 hr. MCTR1 treatment markedly inhibited HS degradation by downregulating heparanase (HPA) protein expression in vivo and in vitro. Further analyses indicated that MCTR1 upregulates sirtuin 1 (SIRT1) expression and decreases NF-κB p65 phosphorylation. In the presence of BOC-2 or EX527, the above effects of MCTR1 were abolished. These results suggest that MCTR1 protects against LPS-induced sepsis in mice by attenuating pulmonary endothelial glycocalyx injury via the ALX/SIRT1/NF-κB/HPA pathway.

PCTR1 ameliorates lipopolysaccharide-induced acute inflammation and multiple organ damage via regulation of linoleic acid metabolism by promoting FADS1/FASDS2/ELOV2 expression and reducing PLA2 expression.

Gram-negative bacterial infection causes an excessive inflammatory response and acute organ damage or dysfunction due to its outer membrane component, lipopolysaccharide (LPS). Protectin conjugates in tissue regeneration 1 (PCTR1), an endogenous lipid mediator, exerts fundamental anti-inflammation and pro-resolution during infection. In the present study, we examined the properties of PCTR1 on the systemic inflammatory response, organic morphological damage and dysfunction, and serum metabolic biomarkers in an LPS-induced acute inflammatory mouse model. The results show that PCTR1 reduced serum inflammatory factors and ameliorated morphological damage and dysfunction of the lung, liver, kidney, and ultimately improved the survival rate of LPS-induced acute inflammation in mice. In addition, metabolomics analysis and high performance liquid chromatography-mass spectrometry revealed that LPS-stimulated serum linoleic acid (LA), arachidonic acid (AA), and prostaglandin E2 (PGE2) levels were significantly altered by PCTR1. Moreover, PCTR1 upregulated LPS-inhibited fatty acid desaturase 1 (FADS1), fatty acid desaturase 2 (FADS2), and elongase of very long chain fatty acids 2 (ELOVL2) expression, and downregulated LPS-stimulated phospholipase A2 (PLA2) expression to increase the intrahepatic content of AA. However, these effects of PCTR1 were partially abrogated by a lipoxin A4 receptor (ALX) antagonist (BOC-2). In summary, via the activation of ALX, PCTR1 promotes the conversion of LA to AA through upregulation of FADS1, FADS2, and ELOVL2 expression, and inhibits the conversion of bound AA into free AA through downregulation of PLA2 expression to decrease the serum AA and PGE2 levels.

Lipoxin A4 ameliorates lipopolysaccharide-induced lung injury through stimulating epithelial proliferation, reducing epithelial cell apoptosis and inhibits epithelial-mesenchymal transition.

BACKGROUND: Acute respiratory distress syndrome (ARDS) is characterized by alveolar epithelial disruption. Lipoxins (LXs), as so-called "braking signals" of inflammation, are the first mediators identified to have dual anti-inflammatory and inflammatory pro-resolving properties. METHODS: In vivo, lipoxinA4 was administrated intraperitoneally with 1 µg/per mouse after intra-tracheal LPS administration (10 mg/kg). Apoptosis, proliferation and epithelial-mesenchymal transition of AT II cells were measured by immunofluorescence. In vitro, primary human alveolar type II cells were used to model the effects of lipoxin A4 upon proliferation, apoptosis and epithelial-mesenchymal transition. RESULTS: In vivo, lipoxin A4 markedly promoted alveolar epithelial type II cells (AT II cells) proliferation, inhibited AT II cells apoptosis, reduced cleaved caspase-3 expression and epithelial-mesenchymal transition, with the outcome of attenuated LPS-induced lung injury. In vitro, lipoxin A4 increased primary human alveolar epithelial type II cells (AT II cells) proliferation and reduced LPS induced AT II cells apoptosis. LipoxinA4 also inhibited epithelial mesenchymal transition in response to TGF-ß1, which was lipoxin receptor dependent. In addition, Smad3 inhibitor (Sis3) and PI3K inhibitor (LY294002) treatment abolished the inhibitory effects of lipoxinA4 on the epithelial mesenchymal transition of primary human AT II cells. Lipoxin A4 significantly downregulated the expressions of p-AKT and p-Smad stimulated by TGF-ß1 in primary human AT II cells. CONCLUSION: LipoxinA4 attenuates lung injury via stimulating epithelial cell proliferation, reducing epithelial cell apoptosis and inhibits epithelial-mesenchymal transition.

Maresin1 Alleviates Metabolic Dysfunction in Septic Mice: A 1H NMR-Based Metabolomics Analysis.

Maresin1 (MaR1), a new anti-inflammatory and proresolving lipid mediator, has been proven to exert organ-protective effects in septic animal models. However, the potential mechanisms are still not fully elucidated. In this study, we sought to explore the impact of MaR1 on metabolic dysfunction in cecal ligation and puncture- (CLP-) induced septic mice. We found that MaR1 significantly increased the overall survival rate and attenuated lung and liver injuries in septic mice. In addition, MaR1 markedly reduced the levels of proinflammatory cytokines (TNF-α and IL-6) and alleviated mitochondrial damage. Based on a 1H NMR-based metabolomics analysis, CLP-induced septic mice had increased levels of acetate, pyruvate, and lactate in serum and decreased levels of alanine, aspartate, glutamate, and fumarate in lungs. However, these metabolic disorders, mainly involving energy and amino acid metabolism, can be recovered by MaR1 treatment. Therefore, our results suggest that the protective effects of MaR1 on sepsis could be related to the recovery of metabolic dysfunction and the alleviation of inflammation and mitochondrial damage.

Maresin 1 attenuates mitochondrial dysfunction through the ALX/cAMP/ROS pathway in the cecal ligation and puncture mouse model and sepsis patients.

Inflammation always accompanies infection during sepsis. Mitochondrial dysfunction and the role of reactive oxygen species (ROS) produced by mitochondria have been proposed in the pathogenesis of sepsis. Maresins have protective and resolving effects in experimental models of infection. In the present study, we investigated the effects of maresin 1 (MaR1) on mitochondrial function in cecal ligation and puncture (CLP)-induced sepsis and sepsis patients to identify mechanisms underlying maresin 1-mediated stimulation of ROS in mitochondria. We found that treatment with MaR1 significantly inhibited production of cytokines, decreased bacterial load in the peritoneal lavage fluid, reduced the number of neutrophils, decreased lactic acid level and upregulated cyclic AMP (cAMP) concentration, with the outcome of decreased lung injury in CLP-induced sepsis in mice. The effects of MaR1 on downregulation nitric oxide (NOX) activity, improvement CAT and SOD activity to inhibit ROS production in mitochondria was dependent on lipoxin receptor (ALX) and cAMP. Survival rates were significantly increased after the treatment of mice with MaR1. In BMDM stimulated with LPS, MaR1 inhibited the ROS production, downregulated enzyme activity, reduced mtO2 production, increased mitochondrial membrane potential, improved adenosine triphosphate (ATP) content and mitochondrial DNA (mtDNA) copy number. Finally, the effects of MaR1 on ROS production in the blood of healthy volunteers stimulated with LPS or sepsis patients were associated with ALX and cAMP. Taken together, these data suggest that treatment with MaR1 could attenuate mitochondrial dysfunction during sepsis through regulating ROS production.

Maresin1 stimulates alveolar fluid clearance through the alveolar epithelial sodium channel Na,K-ATPase via the ALX/PI3K/Nedd4-2 pathway.

Maresin1 (MaR1) is a new docosahexaenoic acid-derived pro-resolving agent that promotes the resolution of inflammation. In this study, we sought to investigate the effect and underlining mechanisms of MaR1 in modulating alveolar fluid clearance (AFC) on LPS-induced acute lung injury. MaR1 was injected intravenously or administered by instillation (200 ng/kg) 8 h after LPS (14 mg/kg) administration and AFC was measured in live rats. In primary rat alveolar type II epithelial cells, MaR1 (100 nM) was added to the culture medium with lipopolysaccharide for 6 h. MaR1 markedly stimulated AFC in LPS-induced lung injury, with the outcome of decreased pulmonary edema and lung injury. In addition, rat lung tissue protein was isolated after intervention, and we found MaR1 improved epithelial sodium channel (ENaC), Na,K-adenosine triphosphatase (ATPase) protein expression and Na,K-ATPase activity. MaR1 down-regulated Nedd4-2 protein expression though PI3k/Akt but not though PI3k/SGK1 pathway in vivo. In primary rat alveolar type II epithelial cells stimulated with LPS, MaR1-upregulated ENaC and Na,K-ATPase protein abundance in the plasma membrane. Finally, the lipoxin A4 Receptor inhibitor (BOC-2) and PI3K inhibitor (LY294002) not only blocked MaR1's effects on cAMP/cGMP, the expression of phosphorylated Akt and Nedd4-2, but also inhibited the effect of MaR1 on AFC in vivo. In conclusion, MaR1 stimulates AFC through a mechanism partly dependent on alveolar epithelial ENaC and Na,K-ATPase activation via the ALX/PI3K/Nedd4-2 signaling pathway. Our findings reveal a novel mechanism for pulmonary edema fluid reabsorption and MaR1 may provide a new therapy for the resolution of ALI/ARDS.

Resolvin D1 stimulates alveolar fluid clearance through alveolar epithelial sodium channel, Na,K-ATPase via ALX/cAMP/PI3K pathway in lipopolysaccharide-induced acute lung injury.

Resolvin D1 (7S,8R,17S-trihydroxy-4Z,9E,11E,13Z,15E,19Z-docosahexaenoic acid) (RvD1), generated from ω-3 fatty docosahexaenoic acids, is believed to exert anti-inflammatory properties including inhibition of neutrophil activation and regulating inflammatory cytokines. In this study, we sought to investigate the effect of RvD1 in modulating alveolar fluid clearance (AFC) on LPS-induced acute lung injury. In vivo, RvD1 was injected i.v. (5 µg/kg) 8 h after LPS (20 mg/kg) administration, which markedly stimulated AFC in LPS-induced lung injury, with the outcome of decreased pulmonary edema. In addition, rat lung tissue protein was isolated after intervention and we found RvD1 improved epithelial sodium channel (ENaC) α, γ, Na,K-adenosine triphosphatase (ATPase) α1, ß1 subunit protein expression and Na,K-ATPase activity. In primary rat alveolar type II epithelial cells stimulated with LPS, RvD1 not only upregulated ENaC α, γ and Na,K-ATPase α1 subunits protein expression, but also increased Na+ currents and Na,K-ATPase activity. Finally, protein kinase A and cGMP were not responsible for RvD1's function because a protein kinase A inhibitor (H89) and cGMP inhibitor (Rp-cGMP) did not reduce RvD1's effects. However, the RvD1 receptor (formyl-peptide receptor type 2 [FPR2], also called ALX [the lipoxin A4 receptor]) inhibitor (BOC-2), cAMP inhibitor (Rp-cAMP), and PI3K inhibitor (LY294002) not only blocked RvD1's effects on the expression of ENaC α in vitro, but also inhibited the AFC in vivo. In summary, RvD1 stimulates AFC through a mechanism partly dependent on alveolar epithelial ENaC and Na,K-ATPase activation via the ALX/cAMP/PI3K signaling pathway.

Lipoxin A4 activates alveolar epithelial sodium channel gamma via the microRNA-21/PTEN/AKT pathway in lipopolysaccharide-induced inflammatory lung injury.

Lipoxin A4 (LXA4), as an endogenously produced lipid mediator, promotes the resolution of inflammation. Previously, we demonstrated that LXA4 stimulated alveolar fluid clearance through alveolar epithelial sodium channel gamma (ENaC-γ). In this study, we sought to investigate the mechanisms of LXA4 in modulation of ENaC-γ in lipopolysaccharide (LPS)-induced inflammatory lung injury. miR-21 was upregulated during an LPS challenge and downregulated by LXA4 administration in vivo and in vitro. Serum miR-21 concentration was also elevated in acute respiratory distress syndrome patients as compared with healthy volunteers. LPS increased miR-21 expression by activation of activator protein 1 (AP-1). In A549 cells, miR-21 upregulated phosphorylation of AKT activation via inhibition of phosphatase and tensin homolog (PTEN), and therefore reduced the expression of ENaC-γ. In contrast, LXA4 reversed LPS-inhibited ENaC-γ expression through inhibition of AP-1 and activation of PTEN. In addition, an miR-21 inhibitor mimicked the effects of LXA4; overexpression of miR-21 abolished the protective effects of LXA4. Finally, both AKT and ERK inhibitors (LY294002 and UO126) blocked effects of LPS on the depression of ENaC-γ. However, LXA4 only inhibited LPS-induced phosphorylation of AKT. In summary, LXA4 activates ENaC-γ in part via the miR-21/PTEN/AKT signaling pathway.

CLINICAL VALUE OF SYNDECAN-1 LEVELS IN TRAUMA BRAIN INJURY: A META-ANALYSIS.

ABSTRACT: Background: Traumatic brain injury (TBI) is a head trauma usually associated with death and endothelial glycocalyx damage. Syndecan-1 (SDC-1)-a biomarker of glycocalyx degradation-has rarely been reported in meta-analyses to determine the clinical prognostic value in TBI patients. Methods: We looked into PubMed, EMBASE, Cochrane Library, and Web of Science databases from January 1, 1990, to May 1, 2023, to identify eligible studies. A meta-analysis was conducted using RevMan 5.4 and Stata 16.0 with the search terms "SDC-1" and "traumatic brain injury." Results: The present study included five studies with a total of 640 enrolled patients included. Syndecan-1 concentrations were higher in the isotrauma TBI group than in the non-TBI group (standardized mean difference [SMD] = 0.52; 95% CI: 0.03-1.00; P = 0.04). Subgroup analysis revealed statistical significance when comparing the SDC-1 level of multitrauma TBI (TBI + other injuries) group with the isotrauma TBI group (SMD = 0.74; 95% CI: 0.42-1.05; P < 0.001), and the SDC-1 level of the TBI coagulopathy (+) group (TBI with early coagulopathy) with the TBI coagulopathy (-) group (SMD = 1.75; 95% CI: 0.41-3.10; P = 0.01). Isotrauma TBI patients with higher SDC-1 level were at a higher risk of 30-day in-hospital mortality (odds ratio = 3.32; 95% CI: 1.67-6.60; P = 0.0006). Conclusion: This meta-analysis suggests that SDC-1 could be a biomarker of endotheliopathy and coagulopathy in TBI, as it was increased in isotrauma TBI patients and was higher in multitrauma TBI patients. There is a need for additional research into the use of SDC-1 as a prognostic biomarker in TBI, especially in isotrauma TBI patients.

Cardiac Resolvin D2 ameliorates sepsis-induced cardiomyopathy via inhibiting Caspase-11/GSDMD dependent pyroptosis.

BACKGROUND: Sepsis-induced cardiomyopathy (SICM) is common complication in septic patients with a high mortality and is characterized by an abnormal inflammation response, which was precisely regulated by endogenous specialized pro-resolving mediators (SPMs). However, the metabolic changes of cardiac SPMs during SICM and the roles of SPMs subset in the development of SICM remain unknown. METHODS: In this work, the SPMs concentration was assessed using ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) of SICM mice and SICM patients. The cardiac function was measured by echocardiography after the treatment of a SPMs subset, termed Resolvin D2 (RvD2). Caspase-11-/-, GSDMD-/- and double deficient (Caspase-11-/-GSDMD-/-) mice were used to clarify the mechanisms of RvD2 in SICM. RESULTS: We found that endogenous cardiac SPMs were disorders and RvD2 was decreased significantly and correlated with left ventricular ejection fraction (LVEF) and ß-BNP, cTnT in Lipopolysaccharide/Cecum ligation and puncture (CLP) induced SICM models. Treatment with RvD2 attenuated lethality, cardiac dysfunction and cardiomyocytes death during SICM. Mechanistically, RvD2 alleviated SICM via inhibiting Caspase-11/GSDMD-mediated cardiomyocytes pyroptosis. Finally, the plasma levels of RvD2 were also decreased and significantly correlated with IL-1ß, ß-BNP, cTnT and LVEF in patients with SICM. Of note, plasma RvD2 level is indicator of SICM patients from healthy controls or sepsis patients. CONCLUSION: These findings suggest that decreased cardiac RvD2 may involve in the pathogenesis of SICM. In addition, treatment with RvD2 represents a novel therapeutic strategy for SICM by inhibiting cardiomyocytes pyroptosis.

Efficient pulmonary lymphatic drainage is necessary for inflammation resolution in ARDS.

The lymphatic vasculature is the natural pathway for the resolution of inflammation, yet the role of pulmonary lymphatic drainage function in sepsis-induced acute respiratory distress syndrome (ARDS) remains poorly characterized. In this study, indocyanine green-near infrared lymphatic living imaging was performed to examine pulmonary lymphatic drainage function in septic mouse models. We found that the pulmonary lymphatic drainage was impaired owing to the damaged lymphatic structure in sepsis-induced ARDS. Moreover, prior lymphatic defects by blocking vascular endothelial growth factor receptor-3 (VEGFR-3) worsened sepsis-induced lymphatic dysfunction and inflammation. Posttreatment with vascular endothelial growth factor-C (Cys156Ser) (VEGF-C156S), a ligand of VEGFR-3, ameliorated lymphatic drainage by rejuvenating lymphatics to reduce the pulmonary edema and promote draining of pulmonary macrophages and neutrophils to pretracheal lymph nodes. Meanwhile, VEGF-C156S posttreatment reversed sepsis-inhibited CC chemokine ligand 21 (CCL21), which colocalizes with pulmonary lymphatic vessels. Furthermore, the advantages of VEGF-C156S on the drainage of inflammatory cells and edema fluid were abolished by blocking VEGFR-3 or CCL21. These results suggest that efficient pulmonary lymphatic drainage is necessary for inflammation resolution in ARDS. Our findings offer a therapeutic approach to sepsis-induced ARDS by promoting lymphatic drainage function.